Most new aromatics complexes are designed to maximize the yield of benzene and para-xylene. Benzene is a versatile petrochemical building block used in many different products based on its derivation including ethylbenzene, cumene, and cyclohexane. Para-xylene is also an important building block, which is used almost exclusively for the production of polyester fibers, resins, and films formed via terephthalic acid or dimethyl terephthalate intermediates. Accordingly, an aromatics complex may be configured in many different ways depending on the desired products, available feedstocks, and investment capital available. A wide range of options permits flexibility in varying the product slate balance of benzene and para-xylene to meet downstream processing requirements.
A prior art aromatics complex flow scheme has been disclosed by Meyers in the HANDBOOK OF PETROLEUM REFINING PROCESSES, 2d. Edition in 1997 by McGraw-Hill.
In an aromatics complex, trace olefins from the catalytic reforming unit must be removed or converted. Untreated olefins would contaminate the highly pure aromatics products as well as contaminate catalysts and adsorbents. Further, olefins remaining in the heavy reformate i.e. reformate splitter bottoms, are typically clay treated to remove the olefins. Olefins must be removed from the heavy reformate so that the xylenes sent to the para-xylene column are low in olefins (Bromine Index<20). With heavier reformates, clay life can be as short as 2-3 months. Alternatively, an Olefin Reduction Process (ORP) unit is generally proposed to replace reformate splitter bottoms clay treater to treat olefins.
Moreover, light olefins in the light reformate stream i.e. reformate splitter overhead, are sent to a aromatics extraction unit where most of the light olefins are rejected to the raffinate stream. The traces that remain in the aromatic extract are clay treated prior to fractionation to obtain benzene and toluene. Therefore, besides treating olefins in heavy reformate i.e. reformate splitter bottoms, aromatics complex operators/owners often need to treat olefins in aromatics extraction raffinate and or LPG stream to meet the olefins specification for downstream unit these respective streams feed into.
Generally, in order to meet the meet the product sec on olefins in the raffinate stream, an ORP unit is installed on full reformate stream. Full reformate contains aromatics i.e. benzene, toluene and xylenes in addition to other light reformate and heavy reformate species. If heavy reformate is fed to ORP unit, it saturates about 5-6 wt % benzene and about 0.5 wt % toluene across the unit. This accounts for significant losses across the ORP unit.
Accordingly, it is desirable to provide an improved method and apparatuses for saturation of olefins present in the reformate stream in an aromatic complex. Further, it is desirable to provide a cost-effective method and apparatus to solve the impending problem of olefins present in aromatics extraction raffinate stream. Furthermore, other desirable features and characteristics of the present subject matter will become apparent from the subsequent detailed description of the subject matter and the appended claims, taken in conjunction with the accompanying drawings and this background of the subject matter.